Ok there is a glitch some of u might know this already but i am telling everybody about it. this works on X360 but from what i have heard PS3 also. Follow these steps:
1. have 2 accounts
2. log onto the account that you don't want to beat lou on
3. go to cheats and turn on easy expert, no fail, and hyperspead(set to 2) look on any game website for these cheats if you don't already have them
4. play any song in quickplay on the difficulty that you want to beat lou on
5.when you get into green on the rock meater hit start and then quit when you quit then hit quit to main menu
6. once at main menu log out of the account that you are on and log onto the account that you want to beat lou on
7. start the guitar battle with lou and he should fail in about 5 seconds if you did it correctly.
i know this works on X360 cuz i did it(after i beat him fairly i figured this out so don't be calling me a noob!) (I also beat this game on expert on wii where this glitch doesn't work to prove that too u)
if you need more help see this video:
http://www.youtube.com/watch?v=3aWQeuiLjAI